A receiver tube is a robust, rigid tube, made of steel or other suitable metal that is permanently or semi-permanently affixed to the rear of a vehicle. Its purpose is to accept a sleeve and ball trailer hitch, which is inserted into the receiver, and held there by a laterally extending pin that goes through both the receiver tube and the sleeve and ball hitch. A trailer can then be attached to the hitch.
In order to strengthen a receiver tube, it has, for years, been the practice to affix by welding, a reinforcement collar, made of steel, to the rearward projecting end of the receiver tube. Recently, however, receiver tubes have been designed with integral collars. A typical design of a receiver tube with an integral collar is shown in U.S. Pat. No. 6,408,672 to Roe. In that patent, a receiver tube with an integral collar is produced by inserting a steel tube into the open end of a die conforming to the outer profile of the tube. The die has a cavity shaped like a collar at its outer end, and stop means to prevent movement of the tube longitudinally in the die. The stop means comprises a rigid floor to the die, so that pressure on the tube at the open end of the die will not force the tube through the die. A T-shaped mandrel is then lowered into the tube, with the body of the mandrel conforming to the interior dimension of the tube to support same against collapse under pressure. When the head of the T-shaped mandrel contacts the end of the tube, high pressure is then applied by the mandrel, to deform the end of the tube into the collar shaped cavity. As the mandrel advances, it supports the walls of the tube from deforming. However, as the mandrel advances, the inner end of the tube is substantially unsupported at the moment the head of the mandrel contacts the end of tube. Therefore, in practice, when the method of U.S. Pat. No. 6,408,672 is carried out. Pressure is applied gradually, so that the inner end of the tube, which is supported on its outside, if not on its inside, surfaces, will tend not to buckle. With a faster impact to the outer end of a cold tube, there is a greater tendency for the impact to be absorbed along the entire length of the tube, and so to cause deformation of the partially supported inner end, as well as the unsupported outer end. It will be noted, in this regard, that this tendency is countered to some extent by the closed shape of the tube, which will tend to direct forces outwardly rather than inwardly. However, in this regard, the inner end of the tube may still deform under a high load.